Good that you’ve got something to test with that’s similar , I was meaning what your Mr Fowler guy in America was suggesting. I tried a few variations of dizzy’s after fitting Twin Webers last year. I’d gone from a Vac only 111905205AA dizzy with 0-35deg of advance on a H30/31 Solex. In the end I opted for the 123 as my B type engine should be timed to 0 deg at idle with vac connected and I couldn’t achieve that with a stock SVDA. I was then able to plot my own curve. If your’s is timed higher then you’ll be ok
